Composition Roots and fn(args, deps)

A lot of developers hear "dependency injection" and immediately think of containers, decorators, registration APIs, lifecycle scopes, and framework magic.

That reaction is understandable.

But that association often leads people to overcomplicate a problem that has a much simpler starting point.

At its core, dependency injection just means this:

Pass collaborators in explicitly instead of reaching for them implicitly.

One of the simplest ways to do that in plain TypeScript is this shape:

fn(args, deps)

Where args is call-specific input and deps is the set of collaborators the function needs.

You can read that as: data in, capabilities in.

fn(args, deps) is flexible enough to support composition, testing, and clean application wiring without forcing you into a DI framework.